Professor Sun Yang-guk of the Department of Energy Engineering is February’s Researcher of the Month for his active role in exploring the field of energy engineering. In his paper, “Compositionally Graded Cathode Material with Long-Term Cycling Stability for Electric Vehicles Application”, Sun explains how adding aluminum into the cathode makes batteries last longer and become more stable compared to other rates of composition. The Al-FCG61 that Sun has developed has shown a high rate of energy efficiency even at 100% depth of discharge (DOD), which draws attention in the field.

Sun explains his research with assisted diagrams.

As the supply and demand of the electric vehicle is on the rise, most of the batteries in the market last from 150km to 400km, meaning that once the battery is fully charged, the car would move between the distance within. What accounts for the difference is the capacity as to how much cathode can hold up. In order for cars to go beyond 300km at least, the capacity of the cathode would have to be over 200A/h. The only problem to this is that it gets difficult to make it stable and it could blow up. There are various prototypes ranging from generation 1 to generation 4 and the study carried out in Sun's paper is on generation 3.

Gradients of different components from inner to outer parts of nickel particle. (Photo courtesy of Sun)

Capacity retention, which is the lifespan of a battery, would rise with 61% of nickel with FCG full concentration gradient, which is what Sun has developed in order to create a more stable and long-lasting battery that would hold a larger capacity. Within the mold, Sun has created a two-way particle that contains a high percentage of nickel inside with lower percentage of nickel on the outside. This concentration gradient is created due to the fact that nickel has its advantage of being able to increase the capacity of the battery while it makes the battery more unstable with exothermic reaction. Along with the nickel, Sun has increased the percentage of the manganese inside the particle since it has the advantage of making the cathode more stable.

Depth of discharge (DOD) is the rate at which battery is either charged 60% or 100%, and this is tested before electric vehicles are sold for inspection. The average usage of an electric vehicle is at around 2,500 cycles for 10 years, and the Al-FCG has proven to be more energy efficient even at 100%. Most of the batteries do not last long at DOD100 due to the expansion of volume inside the battery. This means that the battery would lose its efficiency as time goes. Al-FCG has shown its Coulombic efficiency rate of 84.5% even at DOD100, while batteries currently in the market show an average of 50% at 2000 cycles. This new battery devised by Sun is not only more energy efficient, but more cost efficient as well.

Sun wishes to make more efficient batteries.

Sun is continuously researching to keep the DOD level at 100% even after 2000 cycles. With his findings, the electric vehicle industry would definitely benefit hugely in terms of cost and energy efficiency. With different materials, Sun wishes to develop other types of batteries that would bring more comfort to society.